Diabetes remains one of the most serious and under-treated diseases facing the worldwide healthcare system. Diabetes is a chronic disease where the body fails to maintain normal levels of glucose in the bloodstream. It is now the fifth leading cause of death from disease in the U.S. today and accounts for about 15% of the entire healthcare budget. People with diabetes are classified into two groups: Type 1 (formerly known as “juvenile onset” or “insulin dependent” diabetes, that are required to take insulin to maintain life) and Type 2 (formerly known as “adult onset” or “non-insulin dependent,” that may require insulin but may sometimes be treated by diet and oral hypoglycemic drugs). In both cases, without dedicated and regular blood glucose measurement, all patients face the possibility of the complications of diabetes that include cardiovascular disease, kidney failure, blindness, amputation of limbs and premature death.
The number of cases of diabetes in the U.S. has jumped 40% in the last decade. This high rate of growth is believed to be due to a combination of genetic and lifestyle origins that appear to be a long-term trend, including obesity and poor diet. The American Diabetes Association (ADA) and others estimate that about 17 million Americans and over 150 million people worldwide have diabetes, and it is estimated that up to 40% of these people are currently undiagnosed. American Diabetes Association, “Facts & Figures.”
Diabetes must be “controlled” in order to delay the onset of the disease complications. Therefore, it is essential for people with diabetes to measure their blood glucose levels several times per day in an attempt to keep their glucose levels within the normal range (80 to 130 mg/dl). These glucose measurements are used to determine the amount of insulin or alternative treatments necessary to bring the glucose level to within target limits. Self-Monitoring of Blood Glucose (SMBG) is an ongoing process repeated multiple times per day for the rest of the patient's lifetime.
All currently FDA approved invasive or “less-invasive” (blood taken from the arm or other non-fingertip site) glucose monitoring products currently on the market require the drawing of blood in order to make a quantitative measurement of blood glucose. The ongoing and frequent measurement requirements (1 to possibly 10 times per day) presents all diabetic patients with pain, skin trauma, inconvenience, and infection risk resulting in a general reluctance to frequently perform the critical measurements necessary for selecting the appropriate insulin dose or other therapy.
These current product drawbacks have led to a poor rate of patient compliance. Among Type 1 diabetics, 39% measure their glucose levels less than once per day and 21% do not monitor their glucose at all. Among Type 2 diabetics who take insulin, only 26% monitor at least once per day and 47% do not monitor at all. Over 75% of non-insulin-taking Type 2 diabetics never monitor their glucose levels. Roper Starch Worldwide Survey. Of 1,186 diabetics surveyed, 91% showed interest in a non-invasive glucose monitor. [www.childrenwithdiabetes.com] As such, there is both a tremendous interest and clinical need for a non-invasive glucose sensor.
The present invention seeks to replace the currently used blood glucose measurement methods, devices and instruments, including invasive measures and the use of glucose test strips, with an optical non-invasive instrument.
Various methods have been developed related to non-invasive glucose sensing using a dermal testing site such as the finger or earlobe. These methods primarily employ instruments which measure blood-glucose concentration by generating and measuring light only in the near-infrared radiation spectrum. For example, U.S. Pat. No. 4,882,492 (the '492 patent), expressly incorporated by reference herein, is directed to an instrument which transmits near-infrared radiation through a sample to be tested on the skin surface of a human. In the '492 patent, the near-infrared radiation that passes through the sample is split into two beams, wherein one beam is directed through a negative correlation filter and the second through a neutral density filter. The differential light intensity measured through the filters of the two light beams is proportional to glucose concentration according to the '492 patent.
U.S. Pat. No. 5,086,229 (the '229 patent), expressly incorporated by reference herein, is directed to an instrument which generates near-infrared radiation within the spectrum of about 600 to about 1100 nanometers. According to the '229 patent, a person places their finger in between the generated near-infrared radiation source and a detector, which correlates the blood-glucose concentration based on the detected near-infrared radiation. Similarly, U.S. Pat. No. 5,321,265 (the '265 patent), expressly incorporated by reference herein, also measures blood-glucose level using both near-infrared radiation and the fingertip as a testing site. The detectors disclosed in the '265 patent further comprise silicon photocells and broad bandpass filters.
U.S. Pat. No. 5,361,758 (the '758 patent), expressly incorporated by reference herein, is directed to an instrument which measures near-infrared radiation that is either transmitted through or is reflected from the finger or earlobe of a human. In the '758 patent, the transmitted or reflected light is separated by a grating or prism, and the near-infrared radiation is detected and correlated with blood-glucose concentration. This instrument of the '758 patent also comprises an additional timing and control program wherein the device takes measurements specifically in between heartbeats and can also adjust for temperature.
U.S. Pat. No. 5,910,109 (the '109 patent), expressly incorporated by reference herein, is also directed to an instrument for measuring blood-glucose concentration using near-infrared radiation and the earlobe as the testing site. The instrument of the '109 patent comprises four light sources of a very specific near-infrared emission spectrum, and four detectors having specific near-infrared detection spectra corresponding to the wavelength of the light sources. The signals detected by the four distinct detectors are averaged, and these averages are analyzed to determine blood-glucose concentration according to the '109 patent.
The technique of using near-infrared radiation, wherein the near-infrared radiation is transmitted through or reflected from a dermal testing site and monitored for measuring glucose in vivo, is known to be inaccurate. The glucose concentration of interest is in the blood or the interstitial fluid, not on the surface of the dermis. Therefore these methods must penetrate down into the layers beneath the top layers of dermis. There are a number of substances in the dermis that can interfere with the near-infrared glucose signal. Additionally, there is a wide variation in the human dermis, both between individuals and within a given individual. Moreover, glucose simply lacks a satisfactory distinguishable “fingerprint” in the near-infrared radiation spectrum. Because near-infrared radiation is not sufficiently adsorbed by glucose and because of the level of tissue interferences found in the dermis, this technique is substantially less desirable for the accurate measurement of blood-glucose concentrations.
U.S. Pat. No. 6,362,144 (the '144 patent), expressly incorporated by reference herein, discloses using the fingertip as a testing site, however, the described instrument uses attenuated total reflection (ATR) infrared spectroscopy. According to the '144 patent, a selected skin surface, preferably the finger, is contacted with an ATR plate while ideally maintaining the pressure of contact. In the '144 patent, the skin is then irradiated with a mid-infrared beam, wherein said infrared radiation is detected and quantified to measure blood-glucose levels. This technique is not ideal, however, if the surface of tissue from which the measurement is taken is very dense in the wavelength region of interest or is not amenable to direct contact with the ATR plate, such as an eye, nose, mouth, or other orifice, cavity or piercing tract.
The minimal depth of peripheral capillaries in epithelial tissues is typically about 40 microns. Again, there are physical characteristics as well as a number of substances present in the skin that can interfere with the desired glucose-specific signal. While useful in the laboratory, both the near-infrared transmission methods and the ATR method mentioned above are not practical, or may not be adequate for use in monitoring blood glucose concentration in patients.
Methods have also been developed related to non-invasive glucose sensing using the eye as a testing site. For example, in both U.S. Pat. Nos. 3,958,560 (the '560 patent) and 4,014,321 (the '321 patent), both expressly incorporated by reference herein, a device utilizing the optical rotation of polarized light is described. In the '560 and the '321 patents, the light source and light detector are incorporated into a contact lens which is placed on the surface of the eye whereby the eye is scanned using a dual source of polarized radiation, each source transmitting in a different absorption spectrum at one side of the cornea or aqueous humor. The optical rotation of the radiation that passes through the cornea correlates with the glucose concentration in the cornea according to the '560 and '321 patents. While this method would be termed, “non-invasive” because the withdrawal of blood is not required, it may still cause significant discomfort or distort vision of the user because of the need to place the sensor directly on the eye.
U.S. Pat. No. 5,009,230 (the '230 patent), expressly incorporated by reference herein, uses a polarized light beam of near-infrared radiation within the range of 940 to 1000 nm. In the '230 patent, the amount of rotation imparted by glucose present in the bloodstream of the eye on the polarized light beam is measured to determine glucose concentration. Again, the accuracy is limited because glucose simply lacks a sufficiently distinguishable “fingerprint” in this near-infrared radiation spectrum.
Both U.S. Pat. No. 5,209,231 (the '231 patent), and International Publication No. WO 92/07511 (the '511 application), both expressly incorporated by reference herein, similarly disclose the use of polarized light, which is initially split by a beam splitter into a reference beam and a detector beam, and then transmitted through a specimen, preferably the aqueous humor of the eye. The amount of phase shift as compared between the transmitted reference and detector beams are correlated to determine glucose concentration in the '231 patent and '511 application. U.S. Pat. No. 5,535,743 (the '743 patent), expressly incorporated by reference herein, measures diffusely reflected light provided by the surface of the iris as opposed to the aqueous humor of the eye. According to the '743 patent, the measurement of optical absorption is possible whereas measurement of the optical rotation through the aqueous humor is not possible. In the '743 patent, the intensity of the diffusely reflected light, however, may be analyzed to obtain useful information on the optical properties of the aqueous humor, including blood-glucose concentration.
U.S. Pat. No. 5,687,721 (the '721 patent), expressly incorporated by reference herein, also discloses a method of measuring blood-glucose concentration by generating both a measurement and reference polarized light beam, and comparing said beams to determine the angle of rotation, which is attributable to the blood-glucose concentration. The preferable testing site disclosed, however, is the finger or other suitable appendage according to the '721 patent. The '721 patent further discloses and requires the use of a monochromatic laser and/or semi-conductor as a light source.
U.S. Pat. No. 5,788,632 (the '632 patent), expressly incorporated by reference herein, discloses a non-invasive instrument for determining blood-glucose concentration by transmitting a first beam of light through a first polarizer and a first retarder, then directing the light through the sample to be measured, transmitting the light through a second polarizer or retarder, and lastly detecting the light from the second detector. The rotation of measured polarized light is correlated to the blood-glucose concentration of the sample measured according to the '632 patent.
U.S. Pat. No. 5,433,197 (the '197 patent), expressly incorporated by reference herein, discloses a non-invasive instrument for determining blood-glucose concentration using a broad-band of near-infrared radiation which illuminates the eye in such a manner that the energy passes through the aqueous humor in the anterior chamber of the eye and is then reflected from the iris. The reflected energy then passes back through the aqueous humor and the cornea and is collected for spectral analysis. According to the '197 patent, the electrical signals representative of the reflected energy are analyzed by univariate and/or multivariate signal processing techniques to correct for any errors in the glucose determination. Again, the accuracy of the instrument in the '197 patent is limited because glucose simply lacks a sufficiently distinguishable “fingerprint” in this near-infrared radiation spectrum.
Instruments and methods of using the body's naturally emitted radiation to measure blood-glucose concentration using the human body, and in particular, the tympanic membrane as a testing site have also been disclosed. U.S. Pat. Nos. 4,790,324; 4,797,840; 4,932,789; 5,024,533; 5,167,235; 5,169,235; and 5,178,464, expressly incorporated by reference herein, describe various designs, stabilization techniques and calibration techniques for tympanic non-contact thermometers. In addition, U.S. Pat. No. 5,666,956 (the '956 patent), expressly incorporated by reference herein, discloses an instrument which measures electromagnetic radiation from the tympanic membrane and computes monochromatic emissivity using Plank's law by measuring the radiation intensity, spectral distribution, and blackbody temperature. According to the '956 patent, the resultant monochromatic emissivity is variable depending on the spectral characteristics of the site measured, namely the blood-glucose concentration measured from the tympanic membrane. It should be noted, however, that the '956 patent equates skin surfaces of the body to a “gray-body” rather than a black-body with respect to its monochromatic emissivity. Therefore, according to the '956 patent, the accuracy of such skin surface-based methods utilizing natural black-body emitted radiation is not useful for analyte measurements, as compared to a method of subsurface analysis utilizing natural black-body radiation emitted from the tympanic membrane.
The human body naturally emits from its surfaces infrared radiation whose spectrum, or radiation signature, is modified by the presence, absence or concentration of analytes in the body tissues. The eye is particularly well suited as a testing site to detect this infrared radiation. For example, certain analytes, such as glucose, exhibit a minimal time delay in glucose concentration changes between the eye and the blood, and the eye provides a body surface with few interferences. Cameron et al., (3)2 DIABETES TECHNOL. THER., 202–207 (2001). There is, therefore, in the field of non-invasive blood analyte monitoring, an unmet need for a suitable instrument, and methodologies for using it, to accurately measure analyte concentrations, such as blood glucose concentration, as well as concentrations of other desired analytes, in subjects requiring this type of blood analyte measurement.